1. Field of the Invention
This invention relates to the treatment of ground bauxite ore to produce mechanical particles which possess the activity and mechanical strength required for use as a catalyst, especially the catalyst employed in the known Claus process for producing sulfur from hydrogen sulfide gas. In particular, the invention relates to a process for binding particulate bauxite ore with a specific type of colloidal alumina to produce a pelleted sulfur recovery catalyst.
2. Prior Art
U.S. Pat. No. 3,925,257 to Horzepa et al, which is assigned to the assignee of this application, describes a method for pelletizing ground bauxite ore with a specific type of colloidal alumina, namely colloidal boehmite alumina such as is marketed under the tradenames "Dispal.RTM." and "Catapal.RTM.." The process involves mixing a small amount of the colloidal alumina in dry powdered form with dry calcined bauxite fines, adding acid such as hydrochloric to peptize the colloidal alumina, extruding to form pellets, drying and calcining. Included in the specification of the patent of Horzepa et al under "Field of the Invention" is a summary of the history of attempts to produce pelleted bauxite products suitable for use as a sulfur recovery catalyst. Problems encountered in attempting to adapt well-known colloidal alumina binders to the production of a pelletized bauxite product are discussed. Included in the prior art cited in the Horzepa et al patent is U.S. Pat. No. 2,662,860 to Engel et al. The latter patent describes a process for producing an activated alumina bonded product, suitable for use as a sulfur recovery catalyst, by mixing ground uncalcined bauxite ore with aluminum chloride or aluminum sulfate and water, heating to liberate water and hydrolyze the salt, followed by calcination to produce a product having disclosed utility as a catalyst in the Claus process. Disclosures in the Horzepa et al patent as to the prior art are incorporated herein by reference.
The process of the Horzepa et al patent has resulted in a product meeting the criteria (activity, hardness, etc.) of a catalyst for the Claus process without creating a pollution problem during manufacture or leaving undesirable residues in the product. Production costs, however, leave something to be desired. The starting bauxite ore must be calcined twice, once before it is mixed with alumina such as "Catapal" and again after the green pellets have been prepared. Furthermore, the cost of the binder adds appreciably to the manufacturing costs even though small amounts of binder are required. It was found that binding costs could be reduced significantly and manufacturing expenses further decreased by using aluminum chloride with uncalcined ground bauxite ore substantially as described in the patent of Engel et al. However, a pollution problem of potentially serious magnitude was encountered because of the large quantities of hydrochloric acid that volatilized when the extruded pellets were calcined to activate and harden the product.